1. Field of the Invention
The present invention relates generally to a wireless charging network, and more particularly, to a wireless power receiver and a method for setting a sleep mode in the wireless power receiver that may receive wireless charging power from a wireless power transmitter.
2. Description of the Related Art
A mobile terminal, such as a cellular phone or a Personal Digital Assistant (PDA), is powered by a rechargeable battery, for mobility purposes. In order to charge the battery, electrical energy is supplied to the battery of the mobile terminal using a separate charging device. Typically, the charging device and the battery have separate contact terminals mounted on their outer surfaces, such that they may be electrically connected when their contact terminals contact each other.
Since the contact terminals in this contact charging technique protrude outside, they are apt to be contaminated by foreign substances and exposure to moisture, causing a failure in battery charging.
In order to address these and other disadvantages, wireless charging or contactless charging technologies have been developed and used in many electronic devices.
In the wireless charging technology that uses wireless power transmission/reception, a battery of a mobile phone is automatically charged if the mobile phone is placed on a charging pad without being connected to a charging device via a separate charging connector. Generally, the wireless charging technology is well known to the public in application to wireless electric toothbrushes or cordless electric shavers. The wireless charging technology may increase the waterproof functionalities of electronic devices as it may wirelessly charge the electronic devices. In addition, the wireless charging technology may improve the portability of electronic devices by eliminating the unnecessary wired charger. As a result, the related technologies are expected to significantly evolve even in the coming electric car era.
Wireless charging technologies may be roughly classified into a coil-based electromagnetic induction scheme, a resonance scheme, and a radio radiation scheme (also known as a Radio Frequency (RF)/micro wave radiation scheme) that delivers electrical energy by converting it into microwaves.
To this point, the electromagnetic induction scheme has been primarily used. With the recent successful experiments of wirelessly transmitting power by tens of meters using microwaves, a new era in which all electronic products may be wirelessly charged anytime and anywhere appears to be coming in the near future.
The electromagnetic induction-based power transmission method is a scheme of transmitting power between a primary coil and a secondary coil. An induced current occurs when a magnet moves around a coil. Based on this principle, a transmitter may generate a magnetic field, and a receiver may generate electrical energy as a current is induced due to a change in the magnetic field. This phenomenon is called an electromagnetic induction phenomenon, and the electromagnetic induction-based power transmission method has excellent energy transfer efficiency.
The resonance scheme provides a system in which electricity is wirelessly transferred to an electronic device using the resonance-based power transmission principle even though the electronic device is distanced several meters from a charging device. The wireless charging system is based on the physics concept called ‘resonance’, whereby electromagnetic waves containing electrical energy is caused to resonate. The resonating electrical energy is directly delivered only to an electronic device having a resonant frequency, and the unused electrical energy may be re-absorbed as an electromagnetic field instead of being spread into the air. Therefore, unlike the electromagnetic waves, the electrical energy does not seem to affect nearby machines and human bodies.
Although many studies on the wireless charging scheme have been performed, no standard has been proposed for wireless charging priority, search for a wireless power transmitter/receiver, selection of a communication frequency between a wireless power transmitter and a wireless power receiver, adjustment of wireless power, selection of a matching circuit, and distribution of a communication time for each of wireless power receivers in one charging cycle, for example.
While a wireless power transmitter is charging a wireless power receiver, the wireless power receiver may periodically transmit a dynamic signal to the wireless power transmitter, allowing the wireless power transmitter to adjust its transmission power level. However, the wireless power receiver may transmit the dynamic signal at the same intervals even after the power level is stabilized, causing an unnecessary waste of power.
Accordingly, there is a need for a method and apparatus to prevent the unnecessary waste of power after stabilization of a charging power level of the wireless power receiver.